动态显示可输入的字数

还可以输入15字数js：
function setShowLength(obj, maxlength, id)
{
    var rem = maxlength - obj.value.length;
    var wid = id;
    if (rem < 0){
        rem = 0;
    }
    document.getElementById(wid).innerHTML = "还可以输入" + rem + "字数";
}